Radiation sensitive organic thin film comprising an azulenium salt

ABSTRACT

A radiation sensitive organic thin film comprising a compound which has at least one nucleus of azulanium salt.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to organic coating films which effectively absorbradiation, especially lasers of relatively long wavelengths, to convertinto other energy. More particularly, it relates to a novel organiccoating film suitable as: a photosensitive film for use in anelectrophotographic printer which employs a semiconductor laser as lightsource; an optical disc coating film which permits the writing andreproduction of information with a semiconductor laser; an infrared raycutting filter; and so forth.

2. Description of the Prior Art

The electrophotographic printing system employing a laser as a lightsource reproduces a given information image by modulating the laser beamwith electric signals in response to the original information image, andscanning a photosensitive surface with the modulated laser beam by meansof a galvano-mirror or the like to form an electrostatic latent image,followed by toner development and transferring. Gas lasers such as ahelium-cadmium laser (wavelength 441.6 nm) and a helium-neon laser(wavelength 632.8 nm) have been generally used in this printing system.The photosensitive members for these light sources are thereforesatisfactory if spectral-sensitized up to around 650 nm (sensitized tooperate effectively to rays of wavelengths up to around 650 nm). Suchphotosensitive members so far known include those (1) employing a chargetransfer complex of polyvinylcarbazole with trinitrofluorenone in thephotosensitive layer, (2) employing a vapor-deposited layer of telluriumsensitized with selenium as a photosensitive layer, (3) employing aphotosensitive layer comprising two vapor-deposited films, one being aselenium film formed as a charge transport layer on a conductive layerand the other being a selenium-tellurium film formed on said seleniumfilm, (4) employing cadmium sulfide, as a photosensitive layer,spectral-sensitized with a sensitizing colorant, and (5) employing twophotosensitive layers functioning as a charge generation layercontaining organic pigments and a charge transport layer, respectively,both spectral-sensitized up to a required longer wavelength.

The optical disc coating film can store high density information in theform of spiral or circular tracks of fine pits (e.g. about 1μ) opticallydetectable. For writing information on the disc, the surface of alaser-sensitive layer on the disc is scanned spirally or circularly witha converged laser beam modulated, thereby forming pits at the spotsirradiated with pulses of the laser beam. The laser-sensitive layer canform optically detectable pits by absorbing energy of the laser.According to a heat-mode recording technique, for instance, alaser-sensitive layer absorbs thermal energy of the laser and formssmall depressions (pits) by evaporation or fusing at the sites that haveabsorbed the thermal energy. According to another heat-mode recordingtechnique, pits having an optically detectable density are formed at thespots which have absorbed laser energy.

The information stored on the optical disc can be read by scanning thedisc surface along the track with a laser and detecting opticaldifferences between the pits and the pit-free area. For instance, alaser is irradiated to scan the disc surface along the track and thelaser energy reflected from the disc is monitored with a photodetector.When the pit-free site is irradiated, the output of the photodetector islow; when the pit is irradiated, the laser is reflected sufficientlyfrom an underlying reflecting interface, thereby increasing the outputof the photodetector.

For the recording medium to be used in this type of light, materialscomposed mainly of inorganic substances have been proposed until now,including thin metallic films such as aluminum vapor-deposited films,thin bismuth films, thin tellulium oxide films, and amorphous glassfilms of chalcogenite group compounds.

In recent years, there have been developed semiconductor laser devicesof small size and low cost. Further lasers emitted from these devicescan be directly modulated. However, most of these lasers have awavelength of at least 750 nm. Accordingly, in order to carry outrecording and/or reproduction with such a long-wavelength semiconductorlaser, the laser-sensitive film used should have an absorption maximumin a long wavelength region generally of 750-850 nm.

However, existing laser-sensitive films, in particular those composedmainly of inorganic materials, have high reflectance for laser beams,and hence exhibit lower efficiency of laser energy utilization and poorsensitivity characteristics. In addition, extension of theresponse-wavelength region of these films to 750 nm or longer isdisadvantageous, since these laser-sensitive films become complicated inlayer construction and in particular when these sensitized films areused electrophotographic applications, the sensitizing dyes will befaded by repeated charging and exposing operations.

Such being the case, there have been proposed in recent years organicfilms highly sensitive to rays of wavelengths of 750 nm and longer.Examples of such organic flims are those containing a pyrylium dyedisclosed in U.S. Pat. No. 4,315,983 and "Research Disclosure" No. 20517(May, 1981) and those containing a squarylium dye disclosed in J. Vac.Sci. Technol., 18 (1), 105-109 (January/February, 1981).

Besides these, a report on the photoconductivity of phthalocyaninepigments was presented in "RCA Review", Vol. 23, 413-419 (September1962). Electrophotographic photosensitive members employingphthalocyanine pigments were disclosed in U.S. Pat. Nos. 3,397,086 and3,816,118. Further, disazo pigmentcontaining films disclosed in U.S.Pat. Nos. 3,898,084 and 4,251,613 are also known as an example oflaser-sensitive organic films.

However, organic compounds having absorption maxima in the longerwavelength region are, as a rule, the more unstable, often decomposingwith a slight increase in temperature. In view of these problems andadditionally of various characteristics required for use inelectrophotographic printers or in optical discs, organic filmssensitive to long wavelength rays, hitherto proposed are not necessarilysatisfactory for practical use.

These organic semiconductive materials are easy to synthesize ascompared with inorganic semiconductive materials, and a compoundsensitive to rays of required wavelengths can be synthesized.Electrophotographic photosensitive members having a film of such anorganic semiconductive material on a conductive substrate have anadvantage in better sensitivity to color. However, little organicsemiconductive materials can be used with respect to sensitivity anddurability in practice. Further, there have been developed in recentyears organic semiconductive materials having high sensitivitycharacteristics to long wave length rays of 700 nm or longeraccompanying the development of low output semiconductor laser. However,there has been found no organic semiconductive material having thesatisfactory characteristics.

SUMMARY OF THE INVENTION

The first object of this invention is to provide a novel and usefulorganic coating film.

The second object of this invention is to provide an organic coatingfilm having an absorption band in a long wavelength region, particularlyat 750 nm or longer.

The third object of this invention is to provide an organic coating filmstable to heat.

The fourth object of this invention is to provide an electrophotographicphotosensitive coating film for use in electrophotographic printersemploying a laser as a light source.

The fifth object of this invention is to provide an electrophotographicphotosensitive coating film highly sensitive to a ray of wavelength 750nm or longer.

The sixth object of this invention is to provide a coating film usefulfor optical disc recording.

The seventh object of this invention is to provide an optical discrecording film highly sensitive to a ray of wavelength 750 nm or longerand satisfactory in S/N ratio.

The eighth object of this invention is to provide a novel organicsemiconductive material.

The ninth object of this invention is to provide a novel organicsemiconductive film.

The tenth object of this invention is to provide an electrophotographicphotosensitive member employing a novel organic semiconductive film.

The 11th object of this invention is to provide an electrophotographicphotosensitive member suited to electrophotographic copying machines.

The 12th object of this invention is to provide an electrophotographicphotosensitive member suited to laser-beam-scanning electrophotographicprinters.

The 13th object of this invention is to provide an electrophotographicphotosensitive member highly sensitive to rays of long wavelengths.

These objects of this invention are achieved with a radiation-sensitiveorganic thin film comprising a compound which has at least one nucleusof an azulenium salt.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an infrared spectrum of the compound No. 54 citedlater; FIG. 2 illustrates that of the compound No. 63. FIGS. 3 and 4 aresectional views of preferred optical recording media of this invention.FIG. 5 is an illustration of an embodiment making a record in an opticalrecording medium according to this invention.

FIGS. 6 and 7 are illustrations of visible-infrared absorption spectraof the compound Nos. 78 and 76, respectively, in dichloromethane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In preferred embodiments of this invention, the compound having at leastone azulenium nucleus is represented by the following general formula I,II, or III: ##STR1##

In these formulae, each of R₁ -R₇ represents hydrogen, halogen (e.g.chlorine, bromine, or iodine), or an organic monovalent residue. Whilethe monovalent residue can be selected from a wide variety of radicals,preferred ones thereof are alkyl groups, e.g. methyl, ethyl, n-propyl,isopropyl, n-butyl, t-butyl, n-amyl, n-hexyl, n-octyl, 2-ethylhexyl, andt-octyl; alkoxy groups, e.g. methoxy, ethoxy, propoxy, and butoxy;substituted or unsubstituted aryl groups, e.g. phenyl, tolyl, xylyl,ethylphenyl, methoxyphenyl, ethoxyphenyl, chlorophenyl, nitrophenyl,dimethylaminophenyl, α-naphthyl, and β-naphthyl; substituted orunsubstituted aralkyl groups, e.g. benzyl, 2-phenylethyl,2-phenyl-1-methylethyl, bromobenzyl, 2-bromophenylethyl, methylbenzyl,methoxybenzyl, and nitrobenzyl; acyl groups, e.g. acetyl, propionyl,butyryl, valeryl, benzoyl, toluoyl, naphthoyl, phthaloyl, and furoyl;substituted or unsubstituted amino groups, e.g. amino, dimethylamino,diethylamino, dipropylamino, acetylamino, and benzoylamino; substitutedor unsubstituted styryl groups, e.g. styryl, dimethylaminostyryl,diethylaminostyryl, dipropylaminostyryl, methoxystyryl, ethoxystyryl,and methylstyryl; nitro; hydroxyl; carboxyl; cyano; and substituted orunsubstituted arylazo groups, e.g. phenylazo, α-naphthylazo,β-naphthylazo, dimethylaminophenylazo, chlorophenylazo, nitrophenylazo,methoxyphenylazo, and tolylazo. Of the combinations of R₁ -R₂, R₃ -R₄,R₄ -R₅, R₅ -R₆, and R₆ -R₇, at least one may or may not form asubstituted or unsubstituted aromatic ring, e.g. benzene, naphthalene,chlorobenzene, bromobenzene, methylbenzene, ethylbenzene,methoxybenzene, or ethoxybenzene ring.

Z.sup.⊖ represents an anionic residue; A represents an organic divalentresidue linked by a double bond to the azulenium skeleton. The azuleniumcompounds containing said A of this invention can be represented, forexample, by the following general formulae 1 to 11: Q.sup.⊕ in theformulae represents the following azulenium skeleton and the right-handmoieties, excluding Q.sup.⊕, in the formulae are represented by A.

Azulenium skeleton (Q.sup.⊕): ##STR2##

General formula (1): ##STR3## R₁ to R₇ in this formula are as definedabove.

General formula (2): ##STR4## R₁ to R₇ in this formula are as definedabove.

General formula (3): ##STR5##

Each of R₁ ' to R₇ ' in this formula represents hydrogen, halogen, e.g.chlorine, bromine, or iodine, or an organic monovalent residue, whichcan be selected from a variety of radicals. Preferred examples of theorganic monovalent residues are alkyl groups, e.g. methyl, ethyl,n-propyl, isopropyl, n-butyl, t-butyl, n-amyl, n-hexyl, n-octyl,2-ethylhexyl, and t-octyl; alkoxy groups, e.g. methoxy, ethoxy, propoxy,and butoxy; substituted or unsubstituted aryl groups, e.g. phenyl,tolyl, xylyl, ethylphenyl, methoxyphenyl, ethoxyphenyl, chlorophenyl,nitrophenyl, dimethylaminophenyl, α-naphthyl, and β-naphthyl;substituted or unsubstituted aralkyl groups, e.g. benzyl, 2-phenylethyl,2-phenyl-1-methylethyl, bromobenzyl, 2-bromophenylethyl, methylbenzyl,methoxybenzyl, and nitrobenzyl; acyl groups, e.g. acetyl, propionyl,butyryl, valeryl, benzoyl, naphthoyl, phthaloyl, and furoyl; substitutedor unsubstituted amino groups, e.g. amino, dimethylamino, diethylamino,dipropylamino, acetylamino, and benzoylamino; substituted orunsubstituted styryl groups, e.g. styryl, dimethylaminostyryl,diethylaminostyryl, dipropylaminostyryl, methoxystyryl, ethoxystyryl,and methylstyryl; nitro; hydroxyl; carboxyl; cyano; and substituted orunsubstituted arylazo groups, e.g. phenylazo, α-naphthylazo,β-naphthylazo, dimethylaminophenylazo, chlorophenylazo, nitrophenylazo,methoxyphenylazo, and tolylazo. Of the combinations of R₁ '-R₂ ', R₃'-R₄ ', R₄ '-R₅ ', R₅ '-R₆ ', and R₆ '-R₇ ', at least one may or may notform a substituted or unsubstituted aromatic ring, e.g. benzene,naphthalene, chlorobenzene, bromobenzene, methylbenzene, ethylbenzene,methoxybenzene, or ethoxybenzene. Z.sup.⊖ represents an anionic residue;R₈ represents hydrogen, nitro, cyano, or alkyl (e.g. methyl, ethyl,propyl, or butyl), or aryl (e.g. phenyl, tolyl, or xylyl); and nrepresents an integer of 0, 1, or 2.

General formula (4): ##STR6## R₁ to R₇ and Z.sup.⊖ in this formula areas defined above.

General formula (5): ##STR7##

In this formula, R₁ to R₇, R₁ ' to R₇ ', and Z.sup.⊖ are as definedabove.

General formula (6): ##STR8##

In this formula; X₁ represents a non-metal-atomic group necessary tocomplete a nitrogencontaining heterocyclic ring, e.g. pyridine,thiazole, benzothiazole, naphthothiazole, oxazole, benzoxazole,naphthoxazole, imidazole, benzimidazole, 2-quinoline, 4-quinoline,isoquinoline, or indole ring. This heterocyclic ring may be substitutedby halogen, e.g. chlorine, bromine, or iodine; alkyl, e.g. methyl,ethyl, propyl, or butyl; or aryl, e.g. phenyl, tolyl, or xylyl. R₉represents alkyl, e.g. methyl, ethyl, propyl, or butyl; substitutedalkyl, e.g. 2-hydroxyethyl, 2-methoxyethyl, 2-ethoxyethyl,3-hydroxypropyl, 3-methoxypropyl, 3-ethoxypropyl, 3-chloropropyl,3-bromopropyl, or 3-carboxypropyl; cycloalkyl, e.g. cyclohexyl orcyclopropyl; alkenyl, e.g. allyl; aralkyl, e.g. benzyl, 2-phenylethyl,3-phenylpropyl, 4-phenylbutyl, α-naphthylmethyl, or β-naphthylmethyl;substituted aralkyl, e.g. methylbenzyl, ethylbenzyl, dimethylbenzyl,trimethylbenzyl, chlorobenzyl, or bromobenzyl; aryl, e.g. phenyl, tolyl,xylyl, α-naphthyl, or β-naphthyl; or substituted aryl, e.g.chlorophenyl, dichlorophenyl, trichlorophenyl, ethylphenyl,methoxyphenyl, dimethoxyphenyl, aminophenyl, nitrophenyl, orhydroxyphenyl. Z.sup.⊖ represents an anionic residue; and m representsan integer of 0 or 1.

General formula (7):

    Q.sup.⊕ ═CH--R.sub.10

    Z.sup.⊖

In this formula, R₁₀ represents substituted or unsubstituted aryl, e.g.phenyl, tolyl, xylyl, biphenyl, α-naphthyl, β-naphthyl, anthryl,pyrenyl, methoxyphenyl, dimethoxyphenyl, trimethoxyphenyl, ethoxyphenyl,diethoxyphenyl, chlorophenyl, dichlorophenyl, trichlorophenyl,bromophenyl, dibromophenyl, tribromophenyl, ethylphenyl, diethylphenyl,nitrophenyl, aminophenyl, dimethylaminophenyl, diethylaminophenyl,dibenzylaminophenyl, dipropylaminophenyl, morpholinophenyl,piperidylphenyl, piperazinophenyl, diphenylaminophenyl,acetylaminophenyl, benzoylaminophenyl, acetylphenyl, benzoylphenyl, orcyanophenyl; and Z.sup.⊖ represents an anionic residue.

General formula (8):

    Q.sup.⊕ ═CH--R.sub.11

    Z.sup.⊖

In this formula, R₁₁ represents a monovalent heterocyclic residue, e.g.residue of furan, thiophene, benzofran, thionaphthene, dibenzofuran,carbazole, phenothiazine, phenoxazine, or of pyridine; and Z.sup.⊖represents an anionic residue.

General formula (9): ##STR9##

In this formula, R₁₂ represents hydrogen; alkyl, e.g. methyl, ethyl,propyl, or butyl; or substituted or unsubstituted aryl, e.g. phenyl,tolyl, xylyl, biphenyl, ethylphenyl, chlorophenyl, methoxyphenyl,ethoxyphenyl, nitrophenyl, aminophenyl, dimethylaminophenyl,diethylaminophenyl, acetylaminophenyl, α-naphthyl, β-naphthyl, anthryl,or pyrenyl; and R₁₀ and Z.sup.⊖ are as defined above.

General formula (10):

    Q.sup.⊕ ═CH--C.tbd.C--R.sub.10

    Z.sup.⊖

In this formula, R₁₀ and Z.sup.⊖ are as defined above.

General formula (11): ##STR10##

In this formula; X₂ represents an atomic group necessary to completepyrane, thiopyrane, selenopyrane, benzopyrane, benzothiopyrane,benzoselenopyrane, naphthopyrane, naphthothiopyrane, ornaphthoselenopyrane ring substituted or unsubstituted; l represents aninteger of 0 or 1; Y represents sulfur, oxygen, or selenium; R₁₃ and R₁₄each represent hydrogen, alkyl (e.g. methyl, ethyl, propyl, or butyl),alkoxy (e.g. methoxy, ethoxy, propoxy, or butoxy), substituted orunsubstituted aryl (e.g. phenyl, tolyl, xylyl, chlorophenyl, biphenyl,or methoxyphenyl), substituted or unsubstituted styryl (e.g. styryl,p-methylstyryl, o-chlorostyryl, or p-methoxystyryl), ring-substituted orunsubstituted 4-phenyl-1,3-butadienyl (e.g. 4-phenyl-1,3-butadienyl or4-(p-methylphenyl)-1,3-butadienyl), or a substituted or unsubstitutedheterocyclic residue (e.g. quinolyl, pyridyl, carbazolyl, or furyl); andZ.sup.⊖ represents an anionic residue.

Examples of Z.sup.⊖ in the above general formulae (1)-(11) areperchlorate, fluoroborate, sulfoacetate, iodide, chloride, bromide,p-toluenesulfonate, alkylsulfonates, alkyldisulfonates,benzenedisulfonate, halosulfonates, picrate, tetracyanoethylene, andtetracyanoquinodimethane anionic residues.

Examples of the azulenium compound used in this invention are enumeratedbelow.

Compounds represented by the general formula (1): ##STR11##

Compounds represented by the general formula (1) or (2) can be readilyprepared by reacting azulene compounds with squaric acid or croconicacid in a suitable solvent as described in Angew. Chem. Vol. 78, No. 20,p. 937 (1966).

Compounds represented by the general formula (3) wherein n is 0 can beprepared by (1) heating azulene compounds with a 1-formyl-azulenecompound, which is described in J. Chem. Soc., 1960, p. 501, in asuitable solvent in the presence of a strong acid, (2) mixing azulenecompounds with a 1-ethoxymethyleneazulenium salt in a suitable solventas described in J. Chem. Soc., 1961, pp. 1724-1730, or (3) heatingazulene compounds with 2-hydroxymethylene cyclohexanone in a suitablesolvent in the presence of a strong acid as described in J. Chem. Soc.,1961, p. 359.

Compounds represented by the general formula (3) wherein n is 1 or 2 canbe prepared by mixing azulene compounds with a malondialdehyde orglutacondialdehyde is a suitable solvent in the presence of a strongacid as described in J. Chem. Soc., 1961, pp. 3591-3592.

Compounds represented by the general formula (4) can be readily preparedby heating azulene compounds with glyoxal in a suitable solvent in thepresence of a strong acid as described in J. Chem. Soc., 1961, p. 3588.

Compounds represented by the general formula (5) can be prepared byheating azulene compounds with a 1,3-diformylazulene compound in asuitable solvent in the presence of a strong acid as described in J.Chem. Soc., 1960, p. 501.

Compounds represented by the general formula (6) can be prepared byheating 1-formylazulene compounds with a quaternary ammonium salt ofheterocyclic compound having an active methyl group in a suitablesolvent as described in J. Chem. Soc., 1961, pp. 163-167.

Compounds represented by the general formula (7), (8), (9), or (10) canbe prepared by mixing azulene compounds with the corresponding aldehydecompound in a suitable solvent in the presence of a strong acid asdescribed in J. Chem. Soc., 1958, pp. 1110-1117, ibid., 1960, pp.494-501, and ibid., 1961, pp. 3579-3593.

Compounds represented by the general formula (11) can be prepared byreacting 1-formylazulene compounds with a compound represented by thegeneral formula (12) ##STR12## wherein X₂, Y, R₁₃, R₁₄, Z.sup.⊖, and lare the same as in the general formula (11), in a suitable solvent.

Suitable solvents for the above preparations of compounds of theformulae (1)-(11) are alcohols such as ethanol, butanol, and benzylalcohol; nitriles such as acetonitrile and propionitrile; organiccarboxylic acids such as formic acid, acetic acid, and propionic acid;acid anhydrides such as acetic anhydride; and alicyclic ethers such asdioxane and tetrahydrofuran. Mixed solvents of alcohols such as butanoland benzyl alcohol with aromatic hydrocarbons such as benzene can alsobe used. The reaction temperature can be selected from the range fromroom temperature to the boiling point of solvent used, but is generally80°-120° C., preferably 100°-110° C. The reaction period is generally 10minutes to 1 hour, preferably 20 to 30 minutes.

Referring to typical examples of the above compounds used in thisinvention, preparation procedures are illustrated below.

PREPARATION EXAMPLE 1 (COMPOUND NO. 3)

In 80 ml of n-butanol 1.2 g (0.0105 mole) of3,4-dihydroxy-3-cylobutene-1,2-dione was dissolved by heating withstirring to 100° C. in a 200 ml 3-necked flask.

Then, 3 ml of quinoline, 4.46 g (0.0225 mole) of1,4-dimethyl-7-isopropylazulene, and 30 ml of benzene were addedsuccessively to the solution to start reaction. The reaction wascontinued for 5 hours at 95°-110° C. while adding in parts 45 ml ofbenzene and 30 ml of n-butanol and removing water by azeotropicdistillation therewith.

The reaction mixture was cooled and filtered with suction. The filtercake was washed with 50 ml of n-butanol and then with 100 ml ofmethanol, giving a crude pigment. Twice boiling-filtration thereof with100 ml each of tetrahydrofuran gave 3.7 g of the compound No. 3, yield74.7%, m. p. 237°-239° C. (capillary method).

Anal. Calcd. (%) for C₃₄ H₃₄ O₂ : C 86.02, H 7.23. Found (%): C 85.91, H7.34.

Absorption spectrum in chloroform: λ max=770 nm

PREPARATION EXAMPLE 2 (COMPOUND NO. 12)

A mixture of 1.25 ml of 70% perchloric acid and 7.5 ml of ethanol wasadded to a solution of 0.64 g of azulene in a mixture of 7.5 ml of ethylorthoformate and 15 ml of ethanol at room temperature while stirring.Black needle-like crystals were soon oberved to separate out. Themixture, stirred at room temperature for 40 minutes, was filtered withsuction to give a crude precipitate of the compound No. 12. It was twicerinsed and filtered with 20 ml each of ethanol, suspended in 30 ml ofwater, and filtered after a 30-minute stirring. The filter cake waswashed again with 20 ml of ethanol and dried giving 0.87 g of thecompound No. 12, yield 95%, m. p. 260° C. or higher (capillary method).

Absorption spectrum in dichloromethane: λ max=623 nm

Anal. Calcd. (%) for C₂₁ H₁₅ ClO: C 68.76, H 4.13, Cl 9.66. Found (%): C68.61, H 4.03, Cl 9.34.

PREPARATION EXAMPLE 3 (COMPOUND NO. 13)

A mixture of 1.0 g of azulene, 2.77 g of 3-ethoxymethyleneguaiazuleniumperchlorate, and 47 ml of methanol was refluxed with stirring for 5minutes and allowed to stand overnight. The formed precipitate wasfiltered off, washed with 20 ml of methanol, and dried giving 2.35 g ofa crude product (crude yield: 69%). Recrystallization of 2.0 g of thecrude product from acetonitrile gave 1.3 g of the compound No. 13, m. p.194°-196° C. (capillary method).

Absorption spectrum in methylene chloride: λ max=648 nm

Anal. Calcd. (%) for C₂₆ H₂₅ ClO₄ : C 71.46, H 5.78, Cl 8.11. Found (%):C 71.24, H 5.81, Cl 8.17.

PREPARATION EXAMPLE 4 (COMPOUND NO. 21)

A mixture of 2.4 g of 1,4-dimethyl-7-isopropylazulene, 3.0 g of 40%aqueous glyoxal solution, 50 ml of acetonitrile, and 3.0 ml of 70%perchloric acid was heated with stirring at 75°-80° C. for 4 minutes andleft cooling. The next day, the formed precipitate was filtered off,rinsed with 15 ml of acetonitrile, and dried after filtration, giving1.53 g of the compound No. 21, yield 40.8%, m. p. 260° C. or higher(capillary method).

Absorption spectrum in acetonitrile: λ max=534 nm

Anal. Calcd. (%) for C₃₂ H₃₆ Cl₂ O₈ : C62.03, H 5.87, Cl 11.44. Found(%): C 61.97, H 5.96, Cl 11.78.

PREPARATION EXAMPLE 5 (COMPOUND NO. 26)

A mixture of 1.4 g of 1,3-diformylazulene, 3.0 g of1,4-dimethyl-7-isopropylazulene, and 70 ml of glacial acetic acid washeated with stirring to 105° C.

After addition of 3.4 ml of 70% perchloric acid, the mixture was kept atthe same temperature for 5 minutes and allowed to stand overnight. Theformed precipitate was filtered off, rinsed and filtered once with 10 mlof glacial acetic acid and then twice with 50 ml each of water, anddried giving 2.4 g of a crude product (yield 65%). Recrystallization of2.0 g of the crude product from acetonitrile gave 1.2 g of the compoundNo. 26, m. p. 260° C. or higher (capillary method).

Absorption spectrum in glacial acetic acid: λ max=660 nm

Anal. Calcd. (%) for C₄₂ H₄₂ Cl₂ O₈ : C 67.64, H 5.69, Cl 9.51. Found(%): C 67.76, H 5.78, Cl 9.31.

PREPARATION EXAMPLE 6 (COMPOUND NO. 34)

A mixture of 0.60 g of 1-formyl-5-isopropyl-3,8-dimethylazulene, 0.79 gof 4-methyl-1-ethylquinolinium iodide, 1.8 ml of piperidine, and 22 mlof ethanol was heated with stirring to react at 75°-80° C. for 10minutes and was allowed to stand overnight. Crystals separated out werefiltered off, rinsed and filtered twice with 10 ml each of ethanol, anddried giving 0.72 g of the compound No. 34, yield 55%, m. p. 243°-245°C. (capillary method).

Absorption spectrum in dichloromethane: λ max=644 nm

Anal. Calcd. (%) for C₂₈ H₂₀ IN: C 66.26, H 5.97, N 2,76, I 25.01. Found(%): C 66.34, H 5.81, N 2.71 I 25.14.

PREPARATION EXAMPLE 7 (COMPOUND NO. 39)

A solution of 7.92 g of 1,4-dimethyl-7-isopropylazulene in 400 ml oftetrahydrofuran was added dropwise to a solution of 5.96 g ofp-dimethylaminobenzaldehyde and 10 ml of 70% perchloric acid in 400 mlof tetrahydrofuran at room temperature. The mixture, stirred for 2hours, was allowed to stand overnight. The formed precipitate wasfiltered off, rinsed and filtered three times with 100 ml each oftetrahydrofuran, then twice with 200 ml each of water, and further oncewith 100 ml of tetrahydrofuran, and dried giving 10.40 g of the compoundNo. 39, yield 60.6%, m. p. 160.5°-162° C. (capillary method).

Absorption spectrum in acetone: λ max=640 nm

Anal. Calcd. (%) for C₂₄ H₂₈ ClNO₄ : C 67.04, H 6.58, N 3.26, Cl 8.25.Found (%): C 67.17, H 6.68, N 3.19, Cl 8.16.

PREPARATION EXAMPLE 8 (COMPOUND NO. 50)

A solution of 1.28 g of azulene in 150 ml of acetic acid was addeddropwise to a solution of 1.50 g of p-dimethylaminobenzaldehyde and 5.0ml of 70% perchloric acid in 150 ml of acetic acid at room temperature.After one-hour stirring of the mixture, the resulting precipitate wasfiltered off, washed with 100 ml of acetic acid, suspended in 250 ml ofwater, and filtered again after a 30-minute stirring. After 7 times ofrinse and filtration with 200 ml each of water, the precipitate wasdried giving 2.41 g of the compound No. 50, yield 67.0%, m. p. 260° C.or higher (capillary method).

Absorption spectrum in acetonitrile: λ max=634 nm

Anal. Calcd. (%) for C₁₉ H₁₈ ClNO₄ : C 63.42, H 5.05, N 3.89, Cl 9.85.Found (%): C 64.58, H 5.32, N 4.04, Cl 9.64.

PREPARATION EXAMPLE 9 (COMPOUND NO. 54)

After 2.26 g of N-ethyl-3-formylcarbazole and 2.0 g of guaiazulene (G11004 of Aldrich Chemical Co.) were dissolved in 160 ml oftetrahydrofuran, and 5.0 ml of 70% perchloric acid was added to thesolution at room temperature, were reacted at 60°-65° C. for 10 minutes.The resulting mixture was cooled and allowed to stand for 24 hours. Theformed precipitate was filtered off, and after four times of rinse andfiltration with 40 ml each of tetrahydrofuran, was dried giving 3.37 gof a crude product (yield 66.2%). Recrystallization of 0.9 g of thecrude product from a methyl ethyl ketone-acetonitrile (8:5) mixture gave0.42 g of the compound No. 54, m. p. 206°-208° C. (capillary method).

Absorption spectrum in dichloromethane: λ max=612 nm

Anal. Calcd. (%) for C₃₀ H₃₀ ClNO₄ : C 71.48, H 6.01, N 2.78, Cl 7.03.Found (%): C 72.04, H 6.14, N 2.80, Cl 7.01.

An infrared absorption spectrum of this product is shown in FIG. 1.

PREPARATION EXAMPLE 10 (COMPOUND NO. 63)

A solution of 1.77 g of p-dimethylaminocinnamic aldehyde and 2.0 g ofguaiazulene (G 1100-4 of Aldrich Chemical Co.) in 50 ml of acetic acidwas heated to 103° C. The reaction was conducted at 103°-106° C. for 20minutes by adding 2.0 g of 70% perchloric acid. The product mixture wascooled and allowed to stand for 24 hours. The formed precipitate wasfiltered off, and its rinse and filtration were repeated three timeswith 50 ml each of acetic acid, twice with 250 ml each of water, andfurther twice with 250 ml each of ethanol. The filter cake on dryinggave 1.88 g of the compound No. 63, yield 40.9%.

Absorption spectrum in dichloromethane: λ max=728 nm

Anal. Calcd. (%) for C₂₆ H₃₀ ClNO₄ : C 68.48, H 6.64, N 3.07, Cl 7.77.Found (%): C 68.57, H 6.73, N 3.14, Cl 7.64.

An infrared spectrum of this product is shown in FIG. 2.

PREPARATION EXAMPLE 11 (COMPOUND NO. 68)

A solution of 2.0 g of phenylpropargylaldehyde (P 3100-0 mfd. by AldrichChemical Co.) in 20 ml of acetonitrile was added dropwise to a mixtureof 3.0 g of guaiazulene, 2.5 ml of 70% perchloric acid, and 40 ml ofacetonitrile at room temperature. After 2-hour stirring, the formedprecipitate was filtered off, twice rinsed with 20 ml each ofacetonitrile, and dried giving 3.73 g of the compound No. 68, yield60.0%, m. p. 199°-200° C. (capillary method).

Absorption spectrum in methylene chloride: λ max=501 nm

Anal. Calcd. (%) for C₂₄ H₂₃ ClO₄ : C 70.15, H 5.65, Cl 8.63. Found (%):C 70.06, H 5.74, Cl 8.68.

PREPARATION EXAMPLE 12 (COMPOUND NO. 76)

In 100 ml of glacial acetic acid 3.0 g of1-formyl-3,8-dimethyl-5-isopropylazulene and 4.8 g of2-methyl-4,6-diphenylthiopyrylium perchlorate were reacted at 90°-105°C. for 40 minutes. After cooling of the product mixture, separatedcrystals were filtered off, washed with 50 ml of glacial acid, then with500 ml of water, and further twice with 250 ml each of ethanol, anddried giving 7.0 g of the compound No. 78, yield 93%, decomp. point240°-242° C.

Absorption spectrum in dichloromethane: λ max=743 nm

Anal. Calcd. (%) for C₃₄ H₃₁ ClO₄ S: C 71.49, H 5.48, Cl 6.21. Found(%): C 71.36, H 5.54, Cl 6.29.

PREPARATION EXAMPLE 13 (COMPOUND NO. 78)

In 100 ml of acetic anhydride 3.0 g of1-formyl-3,8-dimethyl-5-isopropylazulene and 4.6 g of4-methyl-2,6-diphenylpyrylium perchlorate were reacted at 80°-90° C. for20 minutes. After cooling, separated crystals were filtered off, washedwith 50 ml of glacial acetic acid, then with 600 ml of water, andfurther twice with 250 ml each of ethanol, and dried giving 6.7 g of thecompound No. 78, yield 91%.

Absorption spectrum in dichloromethane: λ max=686 nm

Anal. Calcd. (%) for C₃₄ H₃₁ ClO₅ : C 73.56, H 5.64, Cl 6.39. Found (%):C 73.43, H 5.80, Cl 6.45.

Films comprising the above azulenium compounds exhibit photoconductivityand accordingly can be used for the following photoconductive layers ofelectrophotographic photosensitive members.

In this invention, electrophotographic photosensitive members can beprepared by vacuum deposition of the above azulenium compounds orapplication of a dispersion thereof in a suitable binder, onelectrically conductive substrates.

In preferred embodiments of this invention, the above photoconductivefilms can be applied as the charge generation layer of anelectrophotographic photosensitive member having two photosensitivelayers which function as a charge generation layer and as a chargetransport layer, respectively.

The charge generation layer is desired to contain the abovephotoconductive compound as much as possible for the purpose ofabsorbing most of the incident light to generate a great number ofcharge carriers. Additionally, the charge generation layer is desirablyas thin as 5μ or less, preferably 0.01-1μ, for the purpose of effectiveinjection of the generated charge carriers into the charge transportlayer without substantial deactivation of the carriers due to therecombination or capture (trapping).

The charge generation layer can be formed, as stated above, by applyinga dispersion of the above azulenium compound in a suitable binder on asubstrate or by vacuum deposition of the compound on a substrate using avacuum deposition apparatus. Suitable binders can be selected from awide variety of insulating resins and from organic photoconductivepolymers such as poly(N-vinylcarbazole), polyvinylanthracene,polyvinylpyrene, and the like. Preferred examples of the binder areinsulating resins such as poly(vinyl butyral), polyarylates (including acondensation polymer of bisphenol A and phthalic acid), polycarbonates,polyesters, phenoxy resins, poly(vinyl acetate), acrylic resins,polyacrylamides, polyamides, polyvinylpyridine, cellulosic resins,urethane resins, epoxy resins, casein, poly(vinyl alcohol), andpolyvinylpyrrolidone. Contents of the binder resin in the chargegeneration layer are up to 80%, preferably up to 40%, by weight.

Solvents suitable for these resins vary depending upon the kind of resinand it is desirable to select those not dissolving the charge transportlayer or undercoating layer, which will be described later in detail. Asexamples of the solvents, there may be cited alcohols such as methanol,ethanol, and isopropanol; ketones such as acetone, methyl ethyl ketone,and cyclohexanone; amides such as N,N-dimethylformamide andN,N-dimethylacetamide; sulfoxides such as dimethylsulfoxide; ethers suchas tetrahydrofuran, dioxane, and ethylene glycol monomethyl ether;esters such as methyl acetate and ethyl acetate; halogenated aliphatichydrocarbons such as chloroform, methylene chloride, dichloroethylene,carbon tetrachloride, and trichloroethylene; and aromatic hydrocarbonsor halogenated aromatic hydrocarbons such as benzene, toluene, xylene,ligroin, monochlorobenzene, and dichlorobenzene.

The coating can be accomplished by dip coating, spray coating, spinnercoating, bead coating, Meyer bar coating, blade coating, roller coating,curtain coating, and the like. The coating film is dried preferably byheating after the set to touch at room temperature. The heat drying canbe performed at 30°-200° C. for 5 minutes-2 hours with or withoutblowing air.

The charge transport layer, being electrically in communication with thecharge generation layer, has a function of receiving charge carriersfrom the charge generation layer in an electric field and a function oftransporting these charge carriers to its surface. The charge transportlayer may be laminated either on the upper side or the lower side(substrate side) of the charge generation layer, but preferably on theupper side.

A material transporting charge carrier in the charge transport layer(hereinafter, simply referred to as "charge-transporting material") isdesirably substantially insensitive to electromagnetic waves to whichthe charge generation layer is sensitive. The electromagnetic wavesherein referred to mean rays of light in a broad sense including γ-rays,X-rays, ultraviolet rays, visible rays, near-infrared rays, infraredrays, far infrared rays, etc. When the wavelength region of rays towhich the charge transport layer is sensitive agrees or overlaps withthat of rays to which the charge generation layer is sensitive, thecharge carriers generated in both layers tend to attack each other, thusthe sensitivity lowered.

The charge-transporting materials are classified intoelectron-transporting materials and hole-transporting materials.Electron-transporting materials utilizable in this invention includeelectron attractive materials, e.g. chloranyl, bromanyl,tetracyanoethylene, tetracyanoquinodimethane,2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone,2,4,7-trinitro-9-dicyanomethylenefluorenone, 2,4,5,7-tetranitroxanthone,and 2,4,8-trinitrothioxanthone, and their polymeric materials.

Hole-transporting materials utilizable include pyrene, N-ethylcarbazole,N-isopropylcarbazole,N-methyl-N-phenylhydrazino-3-methylidene-9-ethylcarbazole,N,N-diphenylhydrazino-3-methylidene-9-ethylcarbazole,N,N-diphenylhydrazino-3-methylidene-10-ethylphenothiazine,N,N-diphenylhydrazino-3-methylidene-10-ethylphenoxazine; hydrazones suchas p-diethylaminobenzaldehyde-N,N-diphenylhydrazone,p-diethylaminobenzaldehyde-N-α-naphthyl-N-phenylhydrazone,pyrrolidinylbenzaldehyde-N,N-diphenylhydrazone,1,3,3-trimethylindolenine-ω-aldehyde-N,N-diphenylhydrazone, andp-diethylaminobenzaldehyde-3-methylbenzthiazolinone-2-hydrazone;2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole; pyrazolines such as1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-[quinolyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-[pyridyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-[6-methoxypyridyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-[pyridyl(3)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-[lepidyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-[pyridyl(2)]-3-(p-diethylaminostyryl)-4-methyl-5-(p-diethylaminophenyl)pyrazoline,1-[pyridyl(2)]-3-(α-methyl-p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-phenyl-3-(p-diethylaminostyryl)-4-methyl-5-(p-diethylaminophenyl)pyrazoline,1-phenyl-3-(α-benzyl-p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,and spiropyrazoline; oxazole compounds such as2-(p-diethylaminostyryl)-6-diethylaminobenzoxazole and2-(p-diethylaminophenyl)-4-(p-dimethylaminophenyl)-5-(2-chlorophenyl)oxazole;thiazole compounds such as2-(p-diethylaminostyryl)-6-diethylaminobenzothiazole; triarylmethanecompounds such as bis(4-diethylamino-2-methylphenyl)-phenylmethanepolyarylalkanes such as1,1-bis(4-N,N-diethylamino-2-methylphenyl)heptane and1,1,2,2-tetrakis(4-N,N-dimethylamino-2-methylphenyl)ethane;triphenylamine, poly(N-vinylcarbazole), polyvinylpyrene,polyvinylanthracene, polyvinylacridine, poly(9-vinylphenylanthracene),pyrene-formaldehyde resin, and ethylcarbazole-formaldehyde resin.

Besides these organic charge-transporting materials, such inorganicmaterials as selenium, selenium-tellurium, amorphous silicon, andcadmium sulfide can also be used.

These charge-transporting materials can be used singly or in combinationof two or more.

When the charge-transporting material employed has no film-formingability, its coating film can be formed by mixing with a suitablebinder. Such binders are insulating resins including, for example,acrylic resins, polyarylates, polyesters, polycarbonates, polystyrene,acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer,poly(vinyl butyral), poly(vinyl formal), polysulfone, polyacrylamides,polyamides, and chlorinated rubber; and organic photoconductive polymersincluding, for example, poly(N-vinylcarbazole), polyvinylanthracene, andpolyvinylpyrene.

The charge transport layer cannot be made thicker than necessary becausethe possible charge-carrier transport distance is limited. Its thicknessranges generally from 5 to 30μ, preferably from 8 to 20μ. For formingthe charge transport layer by coating, coating methods as cited abovecan be applied.

The photosensitive layer having a laminate structure comprising suchcharge generation and charge transport layers as stated above is formedon a substrate having a conductive layer. The substrates having aconductive layer include: sheets or films having conductivity inthemselves, such as aluminium, aluminum alloys, copper, zinc, stainlesssteel, vanadium, molybdenum, chrominium, titanium, nickel, indium, gold,and platinum; those of plastics (e.g. polyethylene, polypropylene,poly(vinyl chloride), poly(ethylene terephthalate), acrylic resins,polyfluoroethylene) covered with a film formed by vacuum deposition ofaluminum, aluminum alloy, indium oxide, tin oxide, indium oxide-tinoxide alloy, or the like; those of plastics coated with a dispersion ofconductive particles (e.g. carbon black or silver particles) in asuitable binder; those of plastics and paper impregnated with conductiveparticles; and those of conductive polymers.

An undercoating layer having a barrier function and a bonding functioncan be laid between the conductive layer and the photosensitive layer.The undercoating layer can be formed from casein, poly(vinyl alcohol),nitrocellulose, ethylene-acrylic acid copolymer, polyamides (e.g. nylon6, nylon 66, nylon 610, nylon copolymer, or alkoxymethylated nylon),polyurethanes, gelatin, aluminum oxide, or the like.

Thickness of the undercoating layer is desirably 0.1-5μ, preferably0.5-3μ.

When using a photosensitive member comprising a conductive layer, chargegeneration layer, and charge transport layer laminated in this order, itis necessary to provide positive charge to the surface of the chargetransport layer if this layer is formed from an electron-transportingmaterial. On image exposure of the photosensitive member after thepositive charging, electrons generated in the charge generation layer,in the exposed area, are injected into the charge transport layer, thenarrive at the surface, and neutralize the positive charges, thusdecaying the surface potential and producing an electrostatic contrastto the unexposed area. The thus produced electrostatic latent images, ondevelopment with a negative-working toner, turn into visible images. Thetoner images can be fixed directly or after being transferred to atransfer recording medium such as paper or a plastic film.

It is also possible that the electrostatic latent images on thephotosensitive member are transferred to the insulating layer oftransfer paper, then developed, and fixed. Any of the known developers,development processes, and fixing processes may be adopted, viz. thereare no particular restrictions thereupon. These electrophotographicoperations can be repeated twice or more.

On the other hand, if the charge transport layer is formed from ahole-transporting material, its surface needs to be negatively charged.On image exposure of the photosensitive member after the negativecharging, holes generated in the charge generation layer, in the exposedarea, act similarly to the electrons stated above, thus formingelectrostatic latent images. For developing the latent images, it isnecessary to use a positive-working toner, contrary to the case where anelectron-transporting material is used.

For the image exposure, various radiations can be used including thoseemitted from a halogen lamp, xenon lamp, mercury lamp, and the like aswell as short-pulsed rays such as lasers having a wavelength in thevisible to infrared region, e.g. a gallium-arsenic-aluminumsemiconductor laser (λ=820 nm), argon gas laser (λ=488 nm, 515 nm), andhelium-neon gas laser (λ=632.8 nm); and rays from a xenon flash lamp.

In another embodiment of this invention, the azulenium compounddescribed above can be incorporated as a sensitizer into photosensitivefilms comprising an organic photoconductive material such as theabove-cited hole-transporting material, e.g. hydrazones, pyrazolines,oxazoles, thiazoles, triarylmethanes, polyarylalkanes, triphenylamine,poly(N-vinylcarbazoles), or the like or an inorganic photoconductivematerial such as zinc oxide, cadmium sulfide, selenium, or the like.These photosensitive films are formed by a coating method from mixtures,containing the azulenium compounds, of the above photoconductivematerial and a binder.

Any photosensitive member of this invention contains at least oneazulenium salt selected from the compounds represented by the generalformula (I), (II), or (III) and if necessary, can be improved insensitivity or made panchromatic by incorporating anotherphotoconductive pigment or dye having a different absorption spectrum.

In another embodiment of this invention, the above-mentionedradiation-sensitive film can be used as the optical recording layer ofan optical recording medium, which has a structure, for instance, asshown in FIG. 3 comprising a substrate 1 and an overlying thin film 2containing the above-mentioned organic compound. This thin film 2 can beformed from the compound of the general formula (I), (II), or (III) byvacuum deposition or from a coating liquid containing said compound anda binder by coating. In the case of the coating, the above-mentionedorganic compound contained in the binder may be either in heterogeneousform or in homogeneous form.

Suitable binders for the coating can be selected from a wide variety ofresins including, for example, cellulose esters such as nitrocellulose,cellulose phosphate, cellulose sulfate, cellulose acetate, cellulosepropionate, cellulose butyrate, cellulose myristate, cellulosepalmitate, cellulose acetate-propionate, and cellulose acetate-butyrate;cellulose ethers such as methyl cellulose, ethyl cellulose, propylcellulose, and butyl cellulose; vinyl type resins such as polystyrene,poly(vinyl chloride), poly(vinyl acetate), poly(vinyl butyral),poly(vinyl acetal), poly(vinyl alcohol), and polyvinylpyrrolidone;copolymer resins such as styrene-butadiene copolymer,styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrilecopolymer, and vinyl chloride-vinyl acetate copolymer; acrylic resinssuch as poly(methyl methacrylate), poly(methyl acrylate), poly(butylacrylate), poly(acrylic acid), poly(methacrylic acid), polyacrylamide,and polyacrylonitrile; polyester resins such as poly(ethyleneterephthalate); polyarylate resins such aspoly(4,4'-isopropylidenediphenylene-co-1,4-cyclohexylenedimethylenecarbonate), poly(ethylenedioxy-3,3'-phenylene thiocarbonate),poly(4,4'-isopropylidenediphenylene carbonate-coterephthalate),poly(4,4'-isopropylidenediphenylene carbonate),poly(4,4'-sec-butylidenediphenylene carbonate), andpoly(4,4'-isopropylidenediphenylene carbonate-block-oxyethylene);polyamides; polyimides; epoxy resins; phenolic resins; and polyolefinssuch as polyethylene, polypropylene, and chlorinated polyethylene.

Organic solvents suitable for the coating depend upon the kind of thebinder and whether the above-mentioned compound is intended to be inheterogeneous form or homogenious form in the binder, but the followingsolvents can be generally used: alcohols such as methanol, ethanol, andisopropanol; ketones such as acetone, methyl ethyl ketone, andcyclohexanone; amides such as N,N-dimethylformamide andN,N-dimethylacetamide; sulfoxides such as dimethylsulfoxide; ethers suchas tetrahydrofuran, dioxane, and ethylene glycol monomethyl ether;esters such as methyl acetate, ethyl acetate, and butyl acetate;halogenated aliphatic hydrocarbons such as chloroform, methylenechloride, dichloroethylene, carbon tetrachloride, and trichloroethylene;and aromatic hydrocarbons or chlorinated derivatives thereof, such asbenzene, toluene, xylene, ligroin, monochlorobenzene, anddichlorobenzene.

The coating can be carried out by dip coating, spray coating, spinnercoating, bead coating, Meyer bar coating, blade coating, roller coating,curtain coating and the like.

When forming the film 2 (in FIG. 3) together with a binder, theabove-mentioned organic compound may be contained in the film in amountsof generally 1-90%, preferably 20-70%, by weight. Thickness of the film2, dry coating film or vacuum deposition film, is generally up to 10μ,preferably up to 2μ.

Materials suitable for the substrate 1 include: plastics such aspolyesters, acrylic resins, polyolefin resins, phenolic resins, epoxyresins, polyamides, and polyimides; glass; and metals.

The optical recording medium of this invention, comprising the thin film2 (electromagnetic-radiation-sensitive layer) and its substrate 1, canbe provided with various kinds of auxiliary layer. For example, thesubstrate 1 can be overlaid with an inorganic or organic film for thepurpose of adjusting thermal properties. The radiation-sensitive layer 2can be covered with a protective coating layer of a clear material. Thisprotective coating layer is effective in not only preventing themechanical damage of the thin film 2 but also improving the sensitivitybecause the reflection of incident light can be reasonably inhibitedwith the coat of a proper thickness. Further, as shown in FIG. 4, areflection layer 3 can be provided between the electromagneticradiation-sensitive layer 2 and the substrate 1. This reflection layer 3can be formed by vacuum deposition of a highly reflective metal such asaluminum, silver, or chromium or by laminating a foil of such a metal,on the substrate 1.

The optical recording medium of this invention can be providedpreviously on its surface with pregrooves which function as guiding oraddressing grooves.

In the optical recording medium of this invention, as shown in FIG. 5,pits 5 are formed in the thin film 2 by irradiating it withelectromagnetic radiation 4 or contacting it with a heater. Radiationsources suitable for this purpose include: lasers having a wavelength inthe visible to infrared region, e.g. a gallium-arsenic-aluminumsemiconductor laser (λ=820 nm), argon gas laser (λ=488 nm, 515 nm), andhelium-neon gas laser (λ=632.8 nm); other short pulsed rays from variouslamps such as a xenon flash lamp; and an infrared lamp. The pits differin reflectance from the pit-free area. Hence, pits can be formed on theoptical recording medium by scanning it with pulses of anelectromagnetic radiation along a track, and the difference ofreflectance can be read by means of a photodetector by scanning therecording medium with a low output laser along with the track.

Advantageous effects of the thin film according to this invention are asfollows: The electromagnetic-radiation-sensitive layer exhibits highefficiencies of absorbing electromagnetic radiations, in particular longwavelength lasers. Electrophotographic photosensitive members andoptical recording media provided with this coating film permit imageformation or recording thereupon by use of a semiconductor laser havinga long wavelength as well as a low energy density helium-neon gas laserand rays from a xenon flash lamp. These optical recording media exhibita high S/N ratio and a good reproduction efficiency.

This invention is illustrated in more detail referring to the followingExamples:

EXAMPLES 1 to 25

A solution of casein in aqueous ammonia (casein 11.2 g, 28% aq. ammonia1 g, water 222 ml) was applied to aluminum sheets by means of a Meyerbar and dried to form an intermediate layer 0.1μ thick on each sheet.

25 kinds of coating liquids were prepared by adding 5 g each of 25 kindsof azulenium salts shown in the following table to a solution of 2 g ofa vinyl butyral resin (degree of butyral conversion 63 mole %) in 95 mlof isopropanol.

After dispersing in an attritor, the coating liquids were appliedseparately onto the casein intermediate layers by means of a Meyer barand dried to form charge generation layers each 0.1μ thick.

A solution was prepared by dissolving 5 g of a hydrazone compoundrepresented the formula ##STR13## and 5 g of a poly(methyl methacrylate)resin (number average mol. wt. 100,000) in 70 ml of benzene. Thesolution was applied to the charge generation layers by means of a Meyerbar and dried to form charge transport layers each 12μ thick.

The thus prepared 25 kinds of electrophotographic photosensitive memberswere corona-charged at -5 KV in the static fashion by using anelectrostatic copying paper testing machine (Model SP-428, mfd. byKawaguchi Denki, Co., Ltd.), were retained for 10 seconds in the dark,and exposed to light at an intensity of 5 lux to examine their lightdischarging properties. The results are shown in Table 1, wherein Vo isthe original potential of the charged surface, Vk is the potentialretention (%) after its decaying for 10 seconds in the dark, and E1/2 isthe exposure quantity for halving the potential after decaying for 10seconds in the dark.

                  TABLE 1                                                         ______________________________________                                        Example Azulenium salt                                                                             Vo       Vk   E 1/2                                      No.     (compound No.)                                                                             (-V)     (%)  (lux · sec)                       ______________________________________                                         1       1           570      89    4.5                                        2       2           620      87   10.4                                        3       3           590      90   11.6                                        4       4           580      88    9.2                                        5       9           560      85   18.7                                        6      10           570      89   10.5                                        7      12           600      85    7.4                                        8      13           570      88   16.8                                        9      15           580      86   17.9                                       10      17           590      90   14.6                                       11      21           600      84   35.2                                       12      26           580      89   21.0                                       13      34           590      91    7.8                                       14      39           570      86    4.3                                       15      40           580      89   25.0                                       16      41           560      84   17.5                                       17      42           590      89   21.0                                       18      45           570      88   13.8                                       19      49           600      86   11.3                                       20      50           580      89    7.5                                       21      54           550      84   18.8                                       22      60           590      87   13.5                                       23      61           600      89   18.6                                       24      63           560      91    2.8                                       25      68           570      87   31.4                                       ______________________________________                                    

Unless otherwise noted, light discharging properties of photosensitivemembers in the following Examples were measured as stated above.

EXAMPLE 26

A coating dispersion was prepared by dissolving 5 g of a polyester resin(Vylon 200, mfd. by Toyobo Co., Ltd.) and 5 g of1-[pyridyl-(2)]-3-(4-N,N-diethylaminostyryl)-5-(4-N,N-diethylaminophenyl)pyrazolinein 80 ml of methyl ethyl ketone and dispersing 1.0 g of the azuleniumsalt No. 1 in the solution. The dispersion was applied to an aluminumlayer vapor-deposited on a polyester film and was dried to prepare aphotosensitive member having a photosensitive layer 13μ thick.

Light discharging properties of this photosensitive member were asfollows:

    ______________________________________                                               Vo          -480 V                                                            Vk          82%                                                               E 1/2       28.7 lux · sec                                    ______________________________________                                    

EXAMPLES 27-34 AND 87

Photosensitive members were prepared in the same manner as in Example 26except that azulenium salts shown in the following Table were used inplace of the azulenium salt No. 1. Light discharging properties of thesephotosensitive members are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Example Azulenium salt                                                                             Vo       Vk   E 1/2                                      No.     (compound No.)                                                                             (-V)     (%)  (lux · sec)                       ______________________________________                                        27       2           500      84   29.7                                       28       3           510      88   30.7                                       29      10           470      87   48.3                                       30      12           500      86   28.1                                       31      17           480      84   27.3                                       32      22           510      90   57.0                                       33      34           460      88   40.5                                       34      50           510      87   35.8                                       87      60           500      85   21.2                                       ______________________________________                                    

EXAMPLE 35

A coating dispersion was prepared by adding 1 g ofpoly(N-vinylcarbazole) and 5 mg of the azulenium salt No. 39 to 10 g of1,2-dichloroethane, followed by sufficient stirring. The dispersion wasapplied by doctor blade coating to an aluminum layer vapor-deposited ona poly(ethylene terephthalate) film and was dried to form aphotosensitive layer 15μ thick.

Light discharging properties of the photosensitive member thus preparedwere as follows (positive charging polarity):

    ______________________________________                                               Vo          +470 V                                                            Vk          83%                                                               E 1/2       29.7 lux · sec                                    ______________________________________                                    

EXAMPLE 36

A photosensitive member was prepared in the same manner as in Example 35but using the azulenium salt No. 12 in place of No. 39. Lightdischarging properties of this photosensitive member were as follows(positive charging polarity):

    ______________________________________                                               Vo          +460 V                                                            Vk          81%                                                               E 1/2       35.7 lux · sec                                    ______________________________________                                    

EXAMPLE 37

A coating dispersion was prepared by thoroughly mixing 10 g of finelydivided zinc oxide (Sazex 2000, mfd. by Sakai Chem. Ind. Co., Ltd.), 4 gof an acrylic resin (Dianal LR009, mfd. by Mitsubishi Rayon Co., Ltd.),10 g of toluene, and 10 mg of the azulenium salt No. 20 in a ball mill.The dispersion was applied by doctor blade coating on an aluminum layervapor-deposited on a poly(ethylene terephthalate) film and was dried toprepare a photosensitive member having a photosensitive layer 21μ thick.

The spectral sensitivity of this photosensitive member was measured withan electrophotographic spectrograph. The results indicated that thisphotosensitive layer is sensitive to rays of longer wavelengths ascompared with the same zinc oxide layer but not containing such anazulenium salt.

EXAMPLE 38

A 1.1-μ poly(vinyl alcohol) coat was formed on an aluminum layervapor-deposited on a poly(ethylene terephthalate) film.

A dispersion prepared by mixing 1 wt. part of the azulenium salt No. 3,1 wt. part of a vinyl butyral resin (S-lec BM-2, mfd. by Sekisui Chem.Co., Ltd.), and 30 wt. part of isopropanol in a ball mill for 4 hourswas applied onto the poly(vinyl alcohol) coat by means of a Meyer barand dried to form a charge generation layer 0.1μ thick.

A solution was prepared by dissolving 5 g of a pyrazoline compoundrepresented by the formula ##STR14## and 5 g of a polyarylate resin(product of polycondensation of bisphenol A with a terephthalicacid-isophthalic acid mixture) in 70 ml of tetrahydrofuran was appliedto the charge generation layer and dried to form a charge transportlayer 10μ thick.

Light discharging properties of the photosensitive member thus preparedwere as follows:

    ______________________________________                                               Vo           -560 V                                                           Vk           86%                                                              E 1/2        8.6 lux · sec                                    ______________________________________                                    

EXAMPLE 39

A solution of casein in aqueous ammonia (casein 11.2 g, 28% aqueousammonia 1 g, water 222 ml) was applied to an aluminum cylinder by dipcoating and dried to form an intermediate layer of 1.0 g/m².

The azulenium salt-containing dispersion prepared in Example 38 wasapplied to the intermediate layer and dried to form a charge generationlayer 0.3μ thick.

A solution was prepared by dissolving 1 wt. part ofp-diethylaminobenzaldehyde-N-phenyl-N-α-naphthylhydrazone and 1 wt. partof a polysulfone resin (P 1700, mfd. by Union Carbide Corp.) in 6 wt.parts of monochlorobenzene. The solution was applied to the chargegeneration layer and dried to form a charge transport layer 12μ thick.

Light discharging properties of the photosensitive drum were measured inthe same manner as in Example 1 except that a gallium-aluminum-arsenicsemiconductor laser (λ780 nm) was used as the light source, thepercentage of potential retention, Vk, was measured after 5-second darkdecay, and the exposure quantity E1/2 for halving the potential after5-second dark decay was expressed in the unit microjoule/cm². Theresults were as follows:

    ______________________________________                                               Vo         -520 V                                                             Vk         92%                                                                E 1/2      2.2 μ joule/cm.sup.2                                     ______________________________________                                    

EXAMPLES 40-52

In the same manner as in Example 39, photosensitive drums were preparedand measured for light discharging properties except that azuleniumcompounds shown in Table 3 were used in place of the azulenium salt No.3 for forming the charge generation layers. The results were as shown inTable 3.

                  TABLE 3                                                         ______________________________________                                        Example Azulenium salt                                                                             Vo       Vk   E 1/2                                      No.     compound No. (-V)     (%)  (μjoule/cm.sup.2)                       ______________________________________                                        40       1           530      89   2.1                                        41       2           520      86   2.5                                        42       9           510      87   4.4                                        43      10           540      85   2.0                                        44      12           550      82   6.5                                        45      13           560      84   13.2                                       46      21           550      83   24.6                                       47      25           510      86   16.9                                       48      34           520      88   5.7                                        49      39           580      86   4.9                                        50      50           550      82   6.4                                        51      54           560      84   12.0                                       52      63           550      85   2.3                                        ______________________________________                                    

EXAMPLE 53

A solution of casein in aqueous ammonia was applied to an 100-μ aluminumsheet and dried to form a 1.1-μ undercoat.

A charge-transfer complex was formed by dissolving 5 g of2,4,7-trinitro-9-fluorenone and 5 g of poly(N-vinylcarbazole)(number-average mol. wt. 300,000) in 70 ml of tetrahydrofuran. Thissolution and 1 g of the azulenium salt No. 3 were added to a solution of5 g of a polyester resin (Vylon, mfd. by Toyobo Co., Ltd.) in 70 ml oftetrahydrofuran to form a dispersion, which was applied to the undercoatand dried to form a photosensitive layer 12μ thick.

Light discharging properties of the photosensitive member thus preparedwere measured in the same manner as in Example 39 but by positivecharging. The results were as follows:

    ______________________________________                                               Vo         +460 V                                                             Vk         91%                                                                E 1/2      5.3 μ joule/cm.sup.2                                     ______________________________________                                    

EXAMPLE 54

A 1.1-μ poly(vinyl alcohol) coat was formed on an aluminum layervapor-deposited on a poly(ethylene terephthalate) film.

The same dispersion of the azulenium salt No. 3 as used in Example 38was applied to the poly(vinyl alcohol) coat by means of a Meyer bar anddried to form a charge generation layer 0.5μ thick.

A solution was prepared by dissolving 5 g of a pyrazoline compoundrepresented by the formula ##STR15## and 5 g of a polyarylate resin(product of polycondensation of bisphenol A with a terephthalicacid-isophthalic acid mixture) in 70 ml of tetrahydrofuran. The solutionwas applied to the charge generation layer and dried to form a chargetransport layer 10μ thick.

Light discharging properties of the photosensitive member thus preparedwere measured in the same manner as in Example 39. The results were asfollows:

    ______________________________________                                               Vo         -510 V                                                             Vk         90%                                                                E 1/2      3.2 μ joule/cm.sup.2                                     ______________________________________                                    

EXAMPLES 55-65

Photosensitive members were prepared in the same manner as in Examples1-25 but using 11 kinds of azulenium salts shown in Table 4 for theformation of the charge generation layers. Light discharging propertiesof these photosensitive member were measured in the same manner as inExample 1. The results are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        Example Azulenium salt                                                                             Vo        Vk   E 1/2                                     No.     (compound No.)                                                                             (-V)      (%)  (lux · sec)                      ______________________________________                                        55      72           520       89   10.5                                      56      78           580       76   19.0                                      57      79           535       84   11.4                                      58      77           540       88   10.4                                      59      75           600       70   24.0                                      60      76           500       90   12.5                                      61      81           540       85   14.6                                      62      82           570       87   18.6                                      63      83           490       84    9.5                                      64      84           510       80   10.5                                      65      85           480       85   11.8                                      ______________________________________                                    

EXAMPLE 66

A photosensitive member was prepared in the same manner as in Example 26but using the azulenium salt No. 76 for the formation of the chargegeneration layer. Light discharging properties of this photosensitivemember were as follows:

    ______________________________________                                               Vo           -510 V                                                           Vk           80%                                                              E 1/2        34 lux · sec                                     ______________________________________                                    

EXAMPLES 67-68

Photosensitive members were prepared in the same manner as in Example 35but using the azulenium salt Nos. 78 and 80, respectively. Lightdischarging properties thereof were as follows:

    ______________________________________                                                  Example 67   Example 68                                             ______________________________________                                        Vo          +490 V         +410 V                                             Vk          84%            79%                                                E 1/2       36.8 lux · sec                                                                      32.0 lux · sec                            ______________________________________                                    

EXAMPLE 69

A photosensitive member having a photosensitive layer comprising zincoxide in the same manner as in Example 37 but using the azulenium saltNo. 72 in place of No. 20.

Results of measuring the spectral sensitivity of this photosensitivemember indicated that the photosensitive layer is sensitive to rays oflonger wavelengths as compared with the same zinc oxide layer but notcontaining such an azulenium salt.

EXAMPLE 70

A coating dispersion was prepared by thoroughly mixing 3 wt. parts ofthe azulenium compound No. 3, 12 wt. parts of a nitrocellulose solution(OH--less lacquer, mfd. by Daicel Chem. Industries, Ltd., 25 wt. % ofnitrocellulose in methyl ethyl ketone), and 70 wt. parts of methyl ethylketone. The dispersion was applied by spinner coating to an aluminumlayer vapor-deposited on a glass disc of 30 cm in diameter, and wasdried to form a recording layer of 0.6 g/m².

The thus prepared optical disc recording medium was placed on aturntable, which was then driven at 1000 rpm with a motor. The rotatingdisc was spirally recorded by scanning with 8 MHz pulses of a 5-mWoutput gallium-aluminum-arsenic semiconductor laser (λ=780 nm) convergedto a spot size of 1.0μ in diameter.

The recorded surface of the optical disc, on observation with a scanningelectron microscope, indicated distinct pits. The track of pits wastraced with a low output gallium-aluminum-arsenic semiconductor laserand the reflected beam was detected, giving a sufficiently high S/Nratio.

For the purpose of examining the stability of stored information, therecorded optical disc was allowed to stand for 240 hours under theartificial conditions of 35° C. and 95% R. H., and the surface of thedisc was observed also with a scanning electron microscope. As a result,the same distinct pits as before the stability test were recognized.After the test, the track of pits was again traced with the low outputgallium-aluminum-arsenic semiconductor laser and the reflected beam wasdetected, giving a similarly high S/N ratio as before the stabilitytest.

EXAMPLES 71-80

Optical discs were prepared in the same manner using the same materialsas in Example 70 except that the azulenium compound No. 3 was replacedby the azulenium compound Nos. 13, 21, 26, 34, 39, 50, 54, 63, 68, and76, respectively, and the coating weight of the recording layer waschanged to 0.8 g/m² in Examples 73 and 78.

The optical discs thus prepared were subjected to the sameinformation-writing and reading tests and information-storing stabilitytests as made in Example 70, giving similar good results. That is, inthe information writing tests distinct pits were observed on the discsby means of the scanning electron microscope, in the information readingtests the discs exhibited sufficiently high S/N ratios, and theinformation-storing stability tests proved that the discs maintained theoriginal distinct pits and high S/N ratios.

EXAMPLE 81

A molybdenum boat containing 500 mg of the azulenium compound No. 1 anda glass disc coated with aluminum by vapor deposition were set in avacuum chamber for vapor deposition use. After the chamber was evacuatedto a pressure of 1×10⁻⁶ mmHg or below, the azulenium compound wasvapor-deposited to a thickness of 0.2μ on the aluminum surface whilecontrolling the pressure in the chamber to 1×10⁻⁵ mmHg or below byregulating a heater.

The optical disc recording medium thus prepared was subjected to thesame information-writing and reading tests as in Example 70, exhibitingsimilarly distinct pits and high S/N ratios in the respective tests.

EXAMPLES 82-86

Optical disc recording media were prepared in the same manner as inExample 81 but using the azulenium compound Nos. 4, 8, 12, 27, and 41 inplace of No. 1 for the recording layer.

The optical disc recording media were subjected to the same informationwriting and reading tests as in Example 70, giving good results similarto those in Example 81.

EXAMPLE 88

In the same manner as in Example 39, a photosensitive drum was preparedand measured for light discharging properties except that the azuleniumsalt No. 4 was used in place of the azulenium salt No. 3 for forming thecharge generation layer. The results were as follows:

    ______________________________________                                        Vo                 -530 V                                                     Vk V.sub.5 (V)     92%                                                        E 1/2              1.8 μ joule/cm.sup.2                                    ______________________________________                                    

EXAMPLE 89

A molybdenum boat containing 500 mg of the azulenium compound No. 1 andan aluminum sheet were set in a vacuum chamber for vapor deposition use.After the chamber evacuated to a pressure of 1×10⁻⁶ mmHg or below, theazulenium compound was vapor-deposited on the aluminum sheet to form acharge generation layer 0.2μ thick while controlling the pressure in thechamber to 1×10⁻⁵ mmHg or below by regulating a heater.

The aluminum sheet overlaid with the charge generation layer was set inanother vacuum chamber, which was then evacuated to a pressure of 1×10⁻⁶mmHg or below. Hydrogen gas and silane gas (15 vol% based on thehydrogen were introduced into the chamber, and a glow discharge wasgenerated by applying a 13.5-MHz high-frequency electric field to form acharge transport layer of amorphous silicon 0.3μ thick on the chargegeneration layer.

The photosensitive member thus prepared was set in a charging-exposingtest machine, then corona-charged at ⊖5 KV, and irradiated immediatelythereafter with a pattern of light which was formed by passing the lightof a tungsten lamp through a transmission type of test chart.Immediately thereafter a positive developer (containing a toner and acarrier) was applied to the photosensitive member surface by the cascadetechnique. Thus, a good toner image was obtained on the photosensitivemember surface.

What is claimed is:
 1. A radiation-sensitive organic thin filmcomprising a radiation-sensitive compound having at least one nucleus ofan azulenium salt; said compound represented by the following generalformula I, II or III: ##STR16## wherein; each of R₁, R₂, R₃, R₄, R₅, R₆,and R₇ is hydrogen, halogen, or an organic monovalent residue, where atleast one of the combinations (R₁ and R₂), (R₃ and R₄), (R₄ and R₅), (R₅and R₆), and (R₆ and R₇) may form a substituted or unsubstitutedaromatic ring; A is an organic divalent residue attached through adouble bond to the azulenium nucleus; and Z.sup.⊖ is an anion residue.2. The radiation-sensitive organic thin film of claim 1, wherein saidcompound having at least one nucleus of an azulenium salt is a compoundrepresented by one of the following general formulae (1)-(11): ##STR17##wherein; Q.sup.⊕ is the azulenium residue ##STR18## each of R₁, R₂, R₃,R₄, R₅, R₆, and R₇ is hydrogen, halogen, or an organic monovalentresidue, where at least one of the combinations (R₁ and R₂), (R₃ andR₄), (R₄ and R₅), (R₅ and R₆), and (R₆ and R₇) may form a substituted orunsubstituted aromatic ring;each of R₁ ', R₂ ', R₃ ', R₄ ', R₅ ', R₆ ',and R₇ ' is hydrogen, halogen, or an organic monovalent residue, whereat least one of the combinations (R₁ ' and R₂ '), (R₃ ' and R₄ '), (R₄ 'and R₅ '), (R₅ ' and R₆ '), and (R₆ ' and R₇ ') may form a substitutedor unsubstituted aromatic ring; Z.sup.⊖ is an anionic residue; R₈ ishydrogen, nitro, cyano, alkyl, or aryl; R₉ is substituted orunsubstituted alkyl, substituted or unsubstituted aryl, cycloalkyl,alkenyl, or substituted or unsubstituted aralkyl; R₁₀ is substituted orunsubstituted aryl; R₁₁ is a monovalent heterocyclic residue; R₁₂ ishydrogen, alkyl, substituted or unsubstituted aryl; R₁₃ and R₁₄ each arehydrogen, alkyl, alkoxy, substituted or unsubstituted aryl, substitutedor unsubstituted styryl, ring-substituted or unsubstituted 4-phenyl-1,3-butadienyl or a substituted or unsubstituted heterocyclic residue; X₁is a nonmetal atomic group necessary to complete a nitrogen-containingheterocyclic ring; X₂ is an atomic group necessary to complete pyrane,thiopyrane, selenopyrane, benzopyrane, benzothiopyrane,benzoselenopyrane, naphthopyrane, naphthothiopyrane, ornaphthoselenopyrane ring substituted or unsubstituted; Y is sulfur,oxygen, or selenium; n is an integer of 0, 1, or 2; m is an integer of 0or 1; and l is an integer of 0 or
 1. 3. An electrophotographicphotosensitive member comprising a conductive substrate and aradiation-sensitive organic thin film which comprises aradiation-sensitive compound having at least one nucleus of an azuleniumsalt; said compound represented by the following general formula I, II,or III: ##STR19## wherein; each of R₁, R₂, R₃, R₄, R₅, R₆, and R₇ ishydrogen, halogen, or an organic monovalent residue, where at least oneof the combinations (R₁ and R₂), (R₃ and R₄), (R₄ and R₅), (R₅ and R₆),and (R₆ and R₇) may form a substituted or unsubstituted aromatic ring; Ais an organic divalent residue attached through a double bond to theazulenium nucleus; and Z.sup.⊖ is an anionic residue; and electricproperties of said organic thin film being variable by irradiating withradiation.
 4. The electrophotographic photosensitive member of claim 3,wherein said compound having at least one nucleus of an azulenium saltis a compound represented by one of the following general formulae(1)-(11): R1 ? ? ##STR20## each of R₁, R₂, R₃, R₄, R₅, R₆, and R₇ ishydrogen, halogen, or an organic monovalent residue, where at least oneof the combinations (R₁ and R₂), (R₃ and R₄), (R₄ and R₅), (R₅ and R₆),and (R₆ and R₇) may form a substituted or unsubstituted aromaticring;each of R₁ ', R₂ ', R₃ ', R₄ ', R₅ ', R₆ ', and R₇ ' is hydrogen,halogen, or an organic monovalent residue, where at least one of thecombinations (R₁ ' and R₂ '), (R₃ ' and R₄ '), (R₄ ' and R₅ '), (R₅ 'and R₆ '), and (R₆ ' and R₇ ') may form a substituted or unsubstitutedaromatic ring; Z.sup.⊖ is an anionic residue; R₈ is hydrogen, nitro,cyano, alkyl, or aryl; R₉ is substituted or unsubstituted alkyl,substituted or unsubstituted aryl, cycloalkyl, alkenyl, or substitutedor unsubstituted aralkyl; R₁₀ is substituted or unsubstituted aryl; R₁₁is a monovalent heterocyclic residue; R₁₂ is hydrogen, alkyl, orsubstituted or unsubstituted aryl; R₁₃ and R₁₄ each are hydrogen, alkyl,alkoxy, substituted or unsubstituted aryl, substituted or unsubstitutedstyryl, ring-substituted or unsubstituted 4-phenyl-1,3-butadienyl, or asubstituted or unsubstituted heterocyclic residue; X₁ is a nonmetalatomic group necessary to complete a nitrogen-containing heterocyclicresidue; X₂ is an atomic group necessary to complete pyrane, thiopyrane,selenopyrane, benzopyrane, benzothiopyrane, benzoselenopyrane,naphthopyrane, naphthothiopyrane, or naphthoselenopyrane ringsubstituted or unsubstituted; Y is sulfur, oxygen, or selenium; n is aninteger of 0, 1, or 2; and m is an integer of 0 or
 1. l is an integer of0 or
 1. 5. The electrophotographic photosensitive member of claim 3,wherein said radiation-sensitive organic thin film further comprises abinder.
 6. The electrophotographic photosensitive member of claim 3,wherein said radiation-sensitive organic thin film is contained in acharge generation layer and further comprising a charge transport layerin contact with said charge generation layer.
 7. The electrophotographicphotosensitive member of claim 6, wherein said charge generation layerfurther comprises a binder.
 8. The electrophotographic photosensitivemember of claim 6, wherein said charge transport layer is formed on theopposite side of said charge generation layer from said conductivesubstrate.
 9. The electrophotographic photosensitive member of claim 8,which has an intermediate layer between said charge generation layer andsaid conductive substrate.
 10. The electrophotographic photosensitivemember of claim 6, wherein said charge transport layer comprises ahole-transporting material and a binder.
 11. The electrophotographicphotosensitive member of claim 10, wherein said hole-transportingmaterial is at least one compound selected from the group consisting ofaromatic condensed ring compounds, hydrazones, pyrazolines, oxazoles,thiazoles, triaryl methanes, polyarylalkanes, polyphenylamines, andorganic photoconductive polymers.
 12. The electrophotographicphotosensitive member of claim 11, wherein said hole-transportingmaterial is a hydrazone.
 13. The electrophotographic photosensitivemember of claim 6, wherein said charge transport layer is a thin film ofamorphous silicon.
 14. The electrophotographic photosensitive member ofclaim 6, wherein said charge transport layer comprises a binder and amaterial selected from selenium, cadmium sulfide, and zinc oxide. 15.The electrophotographic photosensitive member of claim 6, wherein saidcharge transport layer is a thin film of selenium.
 16. Theelectrophotographic photosensitive member of claim 3, where saidcompound having at least one nucleus of azulenium salt is a sensitizerfor a photoconductive material.
 17. The electrophotographicphotosensitive member of claim 16, wherein said photoconductive materialis at least one compound selected from the group consisting of aromaticcondensed ring compounds, hydrazones, pyrazolines, oxazoles, thiazoles,triarylmethanes, polyarylalkanes, polyphenylamines, and organicphotoconductive polymers.
 18. The electrophotographic photosensitivemember of claim 3, wherein said radiation is electromagnetic radiationhaving wavelengths belonging to the spectrum from visible light toinfrared.
 19. The electrophotographic photosensitive member of claim 18,wherein said radiation is electromagnetic radiation having wavelengthsbelonging to the spectrum from near-infrared to infrared.
 20. Theelectrophotographic photosensitive member of claim 18, wherein saidradiation is in the form of a laser beam.
 21. The electrophotographicphotosensitive member of claim 19, wherein said radiation is in the formof a laser beam.
 22. The electrophotographic photosensitive member ofclaim 20, wherein said laser beam is emitted from a semiconductor laser.23. An optical recording medium having a radiation-sensitive organicthin film which comprises a radiation-sensitive compound having at leastone nucleus of an azulenium salt; said compound represented by thefollowing general formula I, II or III: ##STR21## wherein; each of R₁,R₂, R₃, R₄, R₅, R₆, and R₇ is hydrogen, halogen, or an organicmonovalent residue, where at least one of the combinations (R₁ and R₂),(R₃ and R₄), (R₄ and R₅), (R₅ and R₆), and (R₆ and R₇) may form asubstituted or unsubstituted aromatic ring; A is an organic divalentresidue attached through a double bond to the azulenium nucleus; andZ.sup.⊖ is an anionic residue; optical properties of said film beingchangeable by irradiating with radiation.
 24. The optical recordingmedium of claim 23, wherein said compound having at least one nucleus ofan azulenium salt is represented by one of the following generalformulae (1)-(11): ##STR22## each of R₁, R₂, R₃, R₄, R₅, R₆, and R₇ ishydrogen, halogen, or an organic monovalent residue, where at least oneof the combinations (R₁ and R₂), (R₃ and R₄), (R₄ and R₅), (R₅ and R₆),and (R₆ and R₇) may form a substituted or unsubstituted aromaticring;each of R₁ ', R₂ ', R₃ ', R₄ ', R₅ ', R₆ ', and R₇ ' is hydrogen,halogen, or an organic monovalent residue, where at least one of thecombinations (R₁ ' and R₂ '), (R₃ ' and R₄ '), (R₄ ' and R₅ '), (R₅ 'and R₆ '), and (R₆ ' and R₇ ') may form a substituted or unsubstitutedaromatic ring. Z.sup.⊖ is an anionic residue; R₈ is hydrogen, nitro,cyano, alkyl, or aryl; R₉ is substituted or unsubstituted alkyl,substituted or unsubstituted aryl, cycloalkyl, alkenyl, or substitutedor unsubstituted aralkyl; R₁₀ is substituted or unsubstituted aryl; R₁₁is a monovalent heterocyclic residue; R₁₂ is hydrogen, alkyl, orsubstituted or unsubstituted aryl; R₁₃ and R₁₄ each are hydrogen, alkyl,alkoxy, substituted or unsubstituted aryl, substituted or unsubstitutedstyryl, ring-substituted or unsubstituted 4-phenyl-1,3-butadienyl, or asubstituted or unsubstituted heterocyclic residue; X₁ is a nonmetalatomic group necessary to complete a nitrogen-containing heterocyclicresidue; X₂ is an atomic group necessary to complete pyrane, thiopyrane,selenopyrane, benzopyrane, benzothiopyrane, benzoselenopyrane,naphthopyrane, naphthothiopyrane, or naphthoselenopyrane ringsubstituted or unsubstituted; Y is sulfur, oxygen, or selenium; n is aninteger of 0, 1, or 2; and m is an integer of 0 or
 1. l is an integer of0 or
 1. 25. The optical recording medium of claim 23, which furthercomprises a substrate and, on the opposite side of saidradiation-sensitive organic thin film, a protective layer.
 26. Theoptical recording medium of claim 23, which further comprises asubstrate and, on the opposite side of said radiation-sensitive organicthin film, a reflection-preventing layer.
 27. The optical recordingmedium of claim 23, which further comprises a substrate and a reflectinglayer provided between said substrate and said radiation-sensitiveorganic thin film.
 28. The optical recording medium of claim 23, whereinsaid radiation-sensitive organic thin film has a pre-groove.
 29. Theoptical recording medium of claim 28, wherein said pre-groove is atracking guide channel.
 30. The optical recording medium of claim 28,wherein said pre-groove is an addressing channel.
 31. The opticalrecording medium of claim 23, wherein pits are produced in saidradiation-sensitive organic thin film by irradiating with radiation. 32.The electrophotographic photosensitive member of claim 16, wherein saidphotoconductive material is an inorganic photoconductive material. 33.The electrophotographic photosensitive member of claim 32, wherein saidinorganic photoconductive material is at least one material selectedfrom the group consisting of selenium, cadmium sulfide, and zinc oxide.34. The electrophotographic photosensitive member of claim 32, whereinsaid inorganic photoconductive material is zinc oxide.